In a statement via its Amaq news service, the IS armed group said one of its “soldiers” carried out the attack on Thursday night “in response to calls to target nations of coalition states that are fighting (the IS armed group)”.
Tunisian Mohamed Lahouaiej-Bouhlel ploughed a 19-tonne truck into a crowd of people in the Riviera city who were celebrating Bastille Day – France’s national day.
At least 10 children and teenagers were among the dead as well as tourists from the United States, Russia, Ukraine, Switzerland and Germany.
French President Francois Hollande met with the country's defence and security chiefs and cabinet ministers as criticism from the opposition and media mounted over security failings after the third major attack in France in 18 months.
A French parliamentary inquiry last week criticised numerous failings by the intelligence services over the Paris attacks.
“We know of course that there are still flaws and shortcomings,” Hollande said.
“Government intervention is imperative in that area in order to better coordinate our intelligence services,” he added.
Presidential contender and former Prime Minister Alain Juppe said on Friday that the latest carnage could have been prevented if “all measures” had been taken.
However, government spokesman Stephane Le Foll slammed Juppe's comments, saying there was as much security present for the fireworks display as there had been for the Euro 2016 football tournament in the city.
He said there were more than 185 police, gendarmes and soldiers on the ground, as well as municipal police and a vast network of surveillance cameras.
“Despite all of that, this man's decisions... created the drama and horror we experienced,” he said.
Hollande said the country would observe three days of mourning as he warned the death toll could rise further, with more than 50 people still fighting for their lives.
Meanwhile, four people linked to Lahouaiej-Bouhlel have been arrested. The driver's estranged wife is also being held by police.
Attacker radicalised very quickly, says Cazeneuve
French Interior Minister Bernard Cazeneuve said on Saturday that the man responsible for the attack in Nice in which 84 people died seemed to have been "radicalised very quickly".
He said that Thursday's massacre was "a new type of attack" which "showed the extreme difficulty of the fight against terrorism".
He also confirmed that Tunisian-born Mohamed Lahouaiej-Bouhlel "had not been known to the intelligence services".
Le Pen calls on Cazeneuve to resign
Marine Le Pen, president of the National Front, called on French interior minister Bernard Cazeneuve to resign following Thursday’s attack in Nice in which 84 people were killed.
“In any other country of the world, a minister with as appalling record as Bernard Cazeneuve – 250 deaths in 18 months – would have resigned,” she said at a press conference at the headquarters of the far right party in Nanterre, just outside Paris.
- with AFP